I’m getting my first snake! Tips?

In two weeks I’ll be welcoming home a juvenile Mexican Black Kingsnake.
I have two enclosures to decide on: a smaller 18”x18”x 18” while he is still small, then upgrade to a 4’ by 2’ by 2’ or just swing for the larger enclosure immediately.
The breeder is Tri Force Morphs, and she recommends the smaller enclosure for now along with paper towels or Reptichip as substrate while he’s little as well. Does anyone have additional advice/experience with a juvenile MB?
I am also not sure on which heating lamp to land on- I decided I’d like to do a heating lamp with a thermostat and also a UV light to try and mimic some sun, are there any tips on which bulb/lamp to get? Or a bundle?
Also the best places to get supplies from such as diet supplements/hides/etc. i have pretty much everything saved and ready to purchase, but any tips for me to take into account would be great!